Is There a Dogtor in the House?

A recent article in Scientific American reports on a new technological development: the electronic nose.  The electronic nose consists of an array of olfactory sensors activated in unique patterns by different aromas.  Software identifies each odor analyzing these patterns.  The technology was originally designed to detect chemical leaks and identify spoiled food, but it may also have diagnostic potential.

We can't help but wonder if this technology was inspired by the work of dogs who have been trained to detect impending seizures, asthma attacks, hypoglycemia and even some cancers.  The dog’s sense of smell is amazing.  Canines can detect chemical constituents in the part per trillion range.  To give you an idea of how incredible this is, consider that one part per trillion corresponds to one minute in 2,000,000 years!

How do they do it?
One theory is that protein molecules called the major histocompatibility complexes (MHCs), exist on the surface of all cells in our bodies. Each individual has a unique combination of the MHCs, making each unique.Besides coding individual identity, MHCs also display fragments of other proteins that are present inside each cell. White blood cells (WBCs) check each cell’s MHC. If the WBCs only see familiar MHCs they ignore them, but if alien fragments, such as those from bacteria or viruses are detected, the WBC will kill the cell to stop the infection from spreading. If the cell has and MHC coding that don’t match the white blood cell’s (as in a transplanted organ) the WBC mistakes it for an infected cell and kills it.

MHCs stick to and display fragments of other proteins.  These fragments don’t ordinarily have an odor but some researches theorize that they may be broken down into smaller, odor-carrying molecules by decay or other metabolic processes or that they aquire odorants in the blood along with the protein fragments. When  the blood serum is processed into urine in the kidneys, the body breaks down the MHCs and releases odorants to the urine. Untreated blood serum has no individual smell because the odorants are still stuck to the MHCs. But once the proteins are digested (by the kidneys, in perspiration or by decay) odorants are free to be detected. 

"This isn't anything magic," says Dr. Larry Myers, associate professor at the Auburn University College of Veterinary Medicine in Auburn, AL.  Dr. Myers has tested the olfactory capabilities of more than 4,000 dogs in the last twenty years.  "Physicians have always used their own senses to determine the presence of absence of disease."  Serpil Erzurum, a pulmonologist at the Cleveland Clinic says that "When you have an exhaled breath, there are all sorts of volatile organic compounds that are produced.  Those compounds are a result of metabolism and, when you have cancer, metabolism changes and the volatile organic compounds are altered.  The changes are detectable by an electronic nose."

Whether it is furry and four-legged or has an electronic display, we look forward to seeing more of these new -- and old -- technologies in the future.